I can't get emission shader to glow in Blender 2.83 Cycles
It's probably best to use a separate glow node just for the lightning in this case:


In the Render Layer options turn on Material Index In your material
under settings use a pass indes that you haven't used for anything
else.
Connect the index MA output to a glow node and add or screen
it back onto the original image.
You can also use the original
colors, if you multiply the image with the mask and let that glow.

Also: the blur node is your friend in this scenario.